Method for producing paper, paperboard and cardboard using an uncrosslinked fixing agent during paper stock draining

ABSTRACT

Paper, board and cardboard are produced by draining paper stock containing interfering substances in the presence of fixing agents by a process in which the fixing agents used are reaction products which are obtainable by reacting amino- and/or ammonium-containing polymers selected from the group consisting of the 
     polymers containing vinylamine units 
     polyalkylene polyamines 
     polyamidoamines 
     ethyleneimine-grafted polyamidoamines which may be crosslinked, 
     polydiallyldimethylammonium chlorides 
     polymers containing dialkylaminoalkylacrylamide units or dialkylaminoalkylmethacrylamide units and 
     polyallylamines and 
     dicyandiamide and formaldehyde condensates 
     with reactive sizes for paper in a weight ratio of polymer to reactive size of from 15,000:1 to 1:1, and the reaction products thus obtainable are used as fixing agents for water-soluble and for water-insoluble interfering substances in the production of paper, board and cardboard from paper stocks containing interfering substances.

The present invention relates to a process for the production of paper,board and cardboard by draining a paper stock, containing interferingsubstances, in the presence of fixing agents.

EP-A-0 438 707 discloses a process for the production of paper, boardand cardboard by draining a paper stock, containing interferingsubstances, in the presence of fixing agents and cationic retentionaids, fixing agents used being hydrolyzed, homo- and/or copolymers ofN-vinylformamide having a degree of hydrolysis of at least 60%. In theproduction of paper, water is used, in practice, and is at leastpartially or completely recycled from the paper machine. This is eitherclarified or unclarified white water or a mixture of such waterqualities. The recycled water contains larger or smaller amounts ofinterfering substances, which are known to impair the efficiency ofcationic retention and draining aids to a very great extent. Theinterfering substances may be water-soluble or colloidal substances andwater-insoluble products.

Owing to the reuse of fibers from waste paper for the production ofpaper, board and cardboard, water-insoluble tacky impurities, ie.stickies and white pitch (binders originating from paper slips), enterthe water circulation of the paper machine and thus cause productionproblems. The tacky impurities are preferentially deposited on wires,felts, rolls and other moving parts of the paper machine. If theprocedure is carried out in the absence of fixing agents as processassistants, the presence of interfering substances may become evident invarious ways. For example, defects form in the paper web, generally inthe form of thin patches or even holes, which may cause tears in thepaper machine or in the printing press.

In addition to resins and lignin components which are dissolved out ofthe wood during fiber production by boiling and mechanical processing,possible sources of interfering substances for stickies are mainlydispersions, natural colloidal systems, such as starch, casein anddextrin, and hotmelt adhesives. Specifically, these are resins, ligninresidues, adhesives from the gluing of book spines, adhesives frompressure-sensitive adhesive labels and envelopes, and white pitch. Thetacky impurities are in most cases removed only to an insufficientextent from the mixture during the processing of waste paper fibers. Inorder to reduce the tack of the undesired impurities, substances havinga large surface area, eg. talc, chalk or bentonite, have long been addedto the paper stock. It is intended thereby substantially to reduce thetack of the tacky impurities, cf. Tappi Press 1990, Vol. 2, pages 508and 512. The disadvantage of this treatment of tacky impurities is thesensitivity to shearing and the limited retention of the particlestreated in this manner in papermaking. Occasionally used dispersants,such as ligninsulfonates, naphthalenesulfonates, nonylphenols oralkoxylated fatty alcohols, prevent agglomeration of stickies to formparticles having a size troublesome for the papermaking process, butconsiderable frothing of the paper stocks occasionally occurs with theuse of these process assistants.

EP-A-0 649 941 discloses a process for controlling the settling of tackyimpurities out of paper stock suspensions. Polymers which containN-vinylformamide units, alkyl-substituted N-vinylcarboxamide units orthe vinylamine units formed therefrom by hydrolysis are used forinhibiting the deposition of white pitch. EP-A-0 061 169 discloses thatcationic polyelectrolytes, which are obtainable by reacting, forexample, polyethyleneimine or polyvinylamine with benzyl chloride orstyrene oxide and in which at least 10% of the aminoalkyl groups carryan aromatic substituent, are used for removing anionic substances fromwater circulations in papermaking.

WO-A-94/12560 discloses condensates of polyalkylenepolyamines, which areobtainable by partial amidation of polyalkyleneamines with carboxylicacids, carboxylic esters, carboxylic anhydrides or carbonyl halides andcrosslinking of the partially amidated polyalkylenepolyamines with atleast bifunctional crosslinking agents, from 0.001 to 10 parts by weightof a crosslinking agent being used per part by weight of the partiallyamidated polyalkylenepolyamines. These condensates are used as drainageaids, flocculants and retention aids and as fixing agents in theproduction of paper.

It is an object of the present invention to provide, for the papermakingprocess, fixing agents which fix both water-soluble interferingsubstances and colloidal interfering substances as well aswater-insoluble tacky impurities to the paper fibers.

We have found that this object is achieved, according to the invention,by a process for the production of paper, board and cardboard bydraining a paper stock, containing interfering substances, in thepresence of fixing agents, the fixing agents used being reactionproducts which are obtainable by reacting amino- and/orammonium-containing polymers selected from the group consisting of the

polymers containing vinylamine units

polyalkylenepolyamines

ethyleneimine-grafted polyamidoamines which may be crosslinked

polydiallyldimethylammonium chlorides

polymers containing dialkylaminoalkylacrylamide units or

dialkylaminomethacrylamide [sic] units and

polyallylamines and

dicyandiamide and formaldehyde condensates

with reactive sizes for paper in a weight ratio of polymer to reactivesize of from 15,000:1 to 1:5.

The present invention furthermore relates to the use of reactionproducts which are obtainable by reacting amino- and/orammonium-containing polymers selected from the group consisting of the

polymers containing vinylamine units

polyalkylenepolyamines

ethyleneimine-grafted polyamidoamines which may be crosslinked,

polydiallyldimethylammonium chlorides

polymers containing dialkylaminoalkylacrylamide units or

dialkylaminomethacrylamide [sic] units and

polyallylamines and

dicyandiamide/formaldehyde condensates

with reactive sizes for paper in a weight ratio of polymer to reactivesize of from 15,000:1 to 1:5, as fixing agents for water-soluble and forwater-insoluble interfering substances in the production of paper, boardand cardboard from paper stocks containing interfering substances.

Suitable fibers for the production of the pulps are all qualitiescommonly used for this purpose, e.g. mechanical pulp, bleached andunbleached chemical pulp and paper stocks obtained from all annualplants. Mechanical pulp includes, for example, groundwood,thermomechanical pulp (TMP), chemothermomechanical pulp (CTMP), pressuregroundwood, semi-chemical pulp, high-yield pulp and refiner mechanicalpulp (RMP). Examples of suitable chemical pulps are sulfate, sulfite andsoda pulps. The unbleached chemical pulps, which are also referred to asunbleached kraft pulp, are preferably used. Suitable annual plants forthe production of paper stocks are, for example, rice, wheat, sugarcaneand kenaf.

Waste paper alone or as a mixture with other fibers is also used for theproduction of the pulps. Waste paper includes coated waste, which, owingto the content of binders for coating and printing inks, gives rise towhite pitch. The adhesives originating from pressure-sensitive adhesivelabels and envelopes and adhesives from the glueing of book binds aswell as hot melts, give rise to the formation of stickies.

The stated fibers can be used alone or as a mixture of one another. Thepulps of the type described above contain varying amounts ofwater-soluble and water-insoluble interfering substances. Interferingsubstances can be quantitatively determined, for example, with the aidof the COD or with the aid of the cationic demand. For the purposes ofthe invention cationic demand is that amount of a cationic polymer whichis necessary to bring a defined amount of the white water to theisoelectric point. Since the cationic demand depends to a very greatextent on the composition of the cationic polymer used in each case forthe determination, a condensate obtained according to Example 3 ofDE-B-2 434 816 and obtainable by grafting a polyamidoamine of adipicacid and diethylenetriamine with ethyleneimine and subsequentlycrosslinking with a polyethylene glycol dichloride ether is used forstandardization. The pulps containing interfering substances have, forexample, a COD of from 300 to 40,000, preferably from 1000 to 30,000, mgof oxygen per kg of the aqueous phase and a cationic demand of more than50 mg of the stated cationic polymer per liter of white water.

The amino- and/or ammonium-containing polymer used as starting materialsfor the preparation of fixing agents are known. They are, for example,synthetic cationic compounds, such as polymers containing vinylamineunits. They are prepared, for example, starting from open-chainN-vinylcarboxamides of the formula

where R¹ and R² may be identical or different and each hydrogen orC₁-C₆-alkyl. Suitable monomers are, for example, N-vinylformamide(R¹=R²=H in formula I), N-vinyl-N-methylformamide, N-vinylacetamide,N-vinyl-N-methylacetamide, N-vinyl-N-ethylacetamide,N-vinyl-N-methylpropionamide and, N-vinylpropionamide. For thepreparation of the polymers, the stated monomers can be polymerizedeither alone, as a mixture of one another or together with othermono-ethylenically unsaturated monomers. Homo- or copolymers ofN-vinylformamide are preferably used as starting materials. Polymerscontaining vinylamine units are disclosed, for example, in U.S. Pat. No.4,421,602, EP-A-02 16 387 and EP-A-0 251 182. They are obtained byhydrolyzing polymers which contain monomers of the formula I aspolymerized units with acids, bases or enzymes.

Suitable monoethylenically unsatured monomers which are copolymerizedwith the N-vinylcarboxamides are all compounds copolymerizabletherewith. Examples of these are vinyl esters of saturated carboxylicacids of from 1 to 6 carbon atoms, such as vinyl formate, vinyl acetate,vinyl propionate and vinyl butyrate, and vinyl ethers, such asC₁-C₆-alkyl vinyl ethers, eg. methyl or ethyl vinyl ether. Furthersuitable comonomers are ethylenically unsaturated C₃-C₆-carboxylicacids, for example acrylic acid, methacrylic acid, maleic acid, crotonicacid, itaconic acid and vinylester [sic] acid, and their alkali metaland alkaline earth metal salts, esters, amides and nitriles of thestated carboxylic acids, for example methyl acrylate, methylmethacrylate, ethyl acrylate and ethyl methacrylate. Further suitablecarboxylic esters are derived from glycols or polyalkylene glycols, onlyone OH group being esterified in each case, eg. hydroxyethyl acrylate,hydroxyethyl methacrylate, hydroxypropyl acrylate, hydroxybutylacrylate, hydroxypropyl methacrylate, hydroxybutyl methacrylate andacrylic monoesters of polyalkylene glycols having a molar mass of from500 to 10,000. Further suitable comonomers are esters of ethylenicallyunsatured carboxylic acids with amino alcohols, for exampledimethylaminoethyl acrylate, dimethylaminoethyl methacrylate,diethylaminoethyl acrylate, diethylaminoethyl methacrylate,dimethylaminopropyl acrylate, dimethylaminopropyl methacrylate,diethylaminopropyl acrylate, dimethylaminobutyl acrylate anddiethylaminobutyl acrylate. The basic acrylates can be used in the formof the free bases, of the salts with mineral acids, such as hydrochloricacid, sulfuric acid or nitric acid, of the salts with organic acids,such as formic acid, acetic acid or propionic acid, or of sulfonic acidsor in quarternized form. Suitable quarternizing agents are for exampledimethyl sulfate, diethyl sulfate, methyl chloride, ethyl chloride andbenzyl chloride.

Further suitable comonomers are amides of ethylenically unsaturatedcarboxylic acids, such as acrylamide and methacrylamide, andN-alkylmonoamides and N-alkyldiamides of monoethylenically unsaturatedcarboxylic acids having alkyl radicals of 1 to 6 carbon atoms, eg.N-methylacrylamide, N,N-dimethylacrylamide, N-methylmethacrylamide,N-ethylacrylamide, N-propylacrylamide and tert-butylacrylamide, andbasic (meth)acrylamides, eg. dimethylaminoethylacrylamide,dimethylaminoethylmethacrylamide, diethylaminoethylacrylamide,diethylaminoethylmethacrylamide, dimethylaminopropylacrylamide,diethylaminopropylacrylamide, dimethylaminopropylmethacrylamide anddiethylaminopropylmethacrylamide.

Other suitable comonomers are N-vinylpyrrolidone, N-vinylcaprolactam,acrylonitrile, methacrylonitrile, N-vinylimidazole and substitutedN-vinylimidazoles, eg. N-vinyl-2-methylimidazole,N-vinyl-4-methylimidazole, N-vinyl-5-methylimidazole,N-vinyl-2-ethylimidazole and N-vinylimidazolines, such asN-vinylimidazoline, N-vinyl-2-methylimidazoline andN-vinyl-2-ethylimidazoline. N-vinylimidazoles and N-vinylimidazolinesare used not only in the form of the free bases but also in the formneutralized with mineral acids or organic acids or in quaternized form,the quaternization preferably being effected with dimethyl sulfate,diethyl sulfate, methyl chloride or benzyl chloride.Diallyldialkylammonium halides, eg. diallyldimethylammonium chlorides[sic], are also suitable.

Other suitable comonomers are sulfo-containing monomers, for examplevinylsulfonic acid, allylsulfonic acid, methallylsulfonic acid,styrenesulfonic acid, the alkali metal and ammonium salts of these acidsand 3-sulfopropyl acrylate. Further modification of the polymerscontaining vinylamine units can be achieved by incorporating, aspolymerized units, up to 5 mol % of units of monomers having at leasttwo ethylenically unsaturated double bonds. Such comonomers are usuallyused as crosslinking agents in copolymerization. The presence of thesecomonomers during the copolymerization results in an increase in themolar masses of the copolymers. Suitable compounds of this type are, forexample, methylenebisacrylamide, esters of acrylic acid and methacrylicacid with polyhydric alcohols, eg. glycol diacrylate, glyceryltriacrylate, glycol dimethacrylate, glyceryl trimethacrylate and otherpolyols, such as pentaerythritol and glucose, which are at leastdiesterified with acrylic acid or methacrylic acid. Suitablecrosslinking agents are also divinylbenzene, divinyldioxane,pentaerythrityl triallyl ether, pentaallylsucrose, divinylurea anddivinylethyleneurea.

The copolymers contain, for example,

from 99 to 1, preferably from 95 to 5 mol-% of N-vinylcarboxamides ofthe formula I and

from 1 to 99, preferably from 5 to 95 mol-% of other monoethylenicallyunsaturated monomers copolymerizable therewith

in polymerized form.

Polymers containing vinylamine units are prepared preferably startingfrom homopolymers of N-vinylformamide or from copolymers which areobtainable by copolymerization of

N-vinylformamide-with

vinyl formate, vinyl acetate, vinyl propionate,

acrylonitrile, N-vinylcaprolactam, N-vinylurea, acrylic acid,

N-vinylpyrrolidone or C₁-C₆-alkyl vinyl ethers

and subsequent hydrolysis of the homo- or copolymers with formation ofvinylamine units from the copolymerized N-vinylformamide units, thehydrolysis being, for example, from 0.1 to 100 mol-%.

The hydrolysis of the above-described polymers is carried out by theaction of acids, bases or enzymes by known methods. Elimination of thegroup

where R² has the meaning stated for R² in the formula I, from thepolymerized monomers of the abovementioned formula I gives polymerscontaining vinylamine units of the formula

where R¹ has the meaning stated in formula I.

The homopolymers of the N-vinylcarboxamides of the formula I and theircopolymers may be hydrolyzed to an extent of from 0.1 to 100, preferablyfrom 1 to 99, mol %. In most cases, the degree of hydrolysis of thehomo- and copolymers is from 5 to 95 mol %. The degree of hydrolysis ofthe homopolymers is equivalent to the content of vinylamine units in thepolymers. In the case of copolymers which contain polymerized vinylester units, hydrolysis of the ester groups with the formation of vinylalcohol units may occur in addition to the hydrolysis of theN-vinylformamide units. This is the case in particular when thehydrolysis of the copolymers is carried out in the presence of sodiumhydroxide solution. Polymerized acrylonitrile units are likewisechemically modified in the hydrolysis. This gives, for example, amidogroups or carboxyl groups. The homo- and copolymers containingvinylamine units may contain up to 20 mol % of amidine units, which areformed, for example, by reaction of formic acid with two neighboringamino groups or by intramolecular reaction of an amino group with aneighboring amido group, for example of a polymerized N-vinylformamideunit. The molar masses of the polymers containing vinylamine units are,for example, from 1000 to 10 million, preferably from 10,000 to 5million (determined by light scattering). This molar mass rangecorresponds, for example, to K values of from 5 to 300, preferably from10 to 250 (determined according to H. Fikentscher in 5% strength aqueoussodium chloride solution at 25° C. and at a polymer concentration of0.5% by weight).

The polymers containing vinylamine units are preferably used insalt-free form. Salt-free aqueous solutions of polymers containingvinylamine units can be prepared, for example, from the salt-containingpolymer solutions described above with the aid of dialysis orultrafiltration through suitable membranes with separation of, foxexample, from 1000 to 500,000, preferably from 10,000 to 300,000,Dalton. The aqueous solutions of amino- and/or ammonium-containing otherpolymers described below can also be obtained in salt-free form with theaid of dialysis or ultrafiltration. Ultrafiltration through membraneshaving the abovementioned separation limits results not only in removalof salts, which are formed, for example, in the hydrolysis of polymerscontaining N-vinylformamide units with acids or bases, but also infractionation of the polymers, so that polymers having a narrower molarmass distribution of M_(w)/M_(n) are obtained. The fractions obtained asresidue in the ultrafiltration and comprising polymers having a narrowdistribution give, on reaction with reactive sizes, reaction productswhich generally have higher efficiency than reaction products which areformed in the reaction of unfractionated polymers of the samecomposition with reactive sizes.

Suitable polyalkylenepolyamines have, for example, molar masses of atleast 1000. Preferably used polyalkylenepolyamines arepolyethyleneimines; they are prepared, for example, by polymerizingethyleneimine in an aqueous solution in the presence of acid-eliminatingcompounds, acids or Lewis acids. Polyethyleneimines have, for example,molar masses of up to 2 million, preferably from 2000 to 1,000,000.Polyethylenimines having molar masses of from 5000 to 800,000 areparticularly preferably used.

Suitable amino- and/or ammonium-containing polymers are alsopolyamidoamines, which are obtainable, for example, by condensation ofdicarboxylic acids with polyamines. Suitable polyamidoamines areobtained, for example, by reacting dicarboxylic acids of 4 to 10 carbonatoms with polyalkylenepolyamines which contain from 3 to 10 basicnitrogen atoms in the molecule. Suitable dicarboxylic acids are forexample, succinic acid, maleic acid, adipic acid, glutaric acid, subericacid, sebacic acid and terephthalic acid. In the preparation of thepolyamidoamines, it is also possible to use mixtures of dicarboxylicacids as well as mixtures of a plurality of polyalkylenepolyamines.Suitable polyalkylenepolyamines are, for example, diethylenetriamine,triethylenetetramine, tetraethylenepentamine, dipropylenetriamine,tripropylenetetramine, dihexamethylenetriamine,aminopropylethylenediamine and bis-aminopropylethylenediamine. For thepreparation of the polyamidoamines, the dicarboxylic acids andpolyalkylenepolyamines are heated to relatively high temperatures, forexample from 120 to 220° C., preferably 130 to 180° C. The water formedin the condensation is removed from the system. Lactones or lactams ofcarboxylic acids of 4 to 8 carbon atoms can, if required, also be usedin the condensation. For example from 0.8 to 1.4 mol of apolyalkylenepolyamine are used per mole of a dicarboxylic acid.

Further amino-containing polymers are ethyleneimine-graftedpolyamidoamines. They are obtainable from the polyamidoamines describedabove by reaction with ethyleneimine in the presence of acids or Lewisacids, such as sulfuric acid or boron trifluoride etherates, at, forexample, from 80 to 100° C. For example, from 1 to 100 parts by weightof ethyleneimine are grafted on per 100 parts by weight of apolyamidoamine. Uncrosslinked polyamidoamines which may be grafted withethyleneimine are preferably used. Compounds of this type are described,for example, in DE-B-24 34 816.

The uncrosslinked or crosslinked polyamidoamines, which may additionallybe grafted with ethyleneimine before the crosslinking, are also suitableas starting material for the preparation of the fixing agents. Thecrosslinked, ethyleneimine-grafted polyamidoamines are water-soluble andhave viscosities from 100 to 2000 mPas, eg. in 25% strength aqueoussolution at 20° C.

Other suitable amino- and/or ammonium-containing polymers for thepreparation of fixing agents are polydiallyldimethylammonium chlorides.Polymers of this type are also known. Both homo- and copolymers ofdiallyldimethylammonium chloride may be used. Suitable comonomers areprimarily acrylamide and/or methacrylamide. The copolymerization can becarried out using any desired monomer ratio. The K value of the homo-and copolymers of diallyldimethylammonium chlorides [sic] is at least30, preferably from 95 to 180.

Other suitable polymers for the preparation of the fixing agents arecopolymers of, for example, from 1 to 99, preferably from 30 to 70, mol% of acrylamide and/or methacrylamide and from 99 to 1, preferably from70 to 30, mol % of dialkylaminoalkylacrylamide and/ordialkylaminoalkylmethacrylamide. The basic acrylamides andmethacrylamides are likewise preferably present in a form neutralizedwith acids or in quaternized form. Examples are

N-trimethylammoniumethylacrylamide chloride,

N-trimethylammoniumethylmethacrylamide chloride,

trimethylammoniumethylacrylamide methosulfate,

trimethylammoniumethylmethacrylamide methosulfate,

N-ethyldimethylammoniumethylacrylamide ethosulfate,

N-ethyldimethylammoniumethylmethacrylamide ethosulfate,

trimethylammoniumpropylacrylamide chloride,

trimethylammoniumpropylmethacrylamide chloride,

trimethylammoniumpropylacrylamide methosulfate,

trimethylammoniumpropylmethacrylamide methosulfate and

N-ethyldimethylammoniumpropylacrylamide ethosulfate.

Trimethylammoniumpropylmethacrylamide chloride is preferred.

Other suitable starting materials for the preparation of the fixingagents are copolymers of from 1 to 99, preferably from 30 to 70, mol %of acrylamide and/or methacrylamide and from 99 to 1, preferably from 70to 30, mol % of dialkylaminoalkyl acrylates and/or methacrylates, eg.copolymers of acrylamide and N,N-dimethylaminoethyl acrylate. Basicacrylates are preferably present in a form neutralized with acids or inquaternized form. Quaternization may be effected, for example, withmethyl chloride or with dimethyl sulfate.

The cationic polymers have, for example, K values of from 30 to 300,preferably from 130 to 180 (determined according to H. Fikentscher in 5%strength aqueous sodium chloride solution at 25° C. and at a polymerconcentration of from 0.5% by weight). At a pH of 4.5, they have, forexample, a charge density of at least 4 meq/g of polyelectrolyte.

Polyallylamines are also suitable cationic polymers which have aminoand/or ammonium groups. Polymers of this type are obtained byhomopolymerization of allylamine, preferably in a form neutralized withacids or in quaternized form, or by copolymerization of allylamine withother monoethylenically unsaturated monomers which are described aboveas comonomers for N-vinylcarboxamides.

The amino- and/or ammonium-containing polymers are modified by reactionwith reactive sizes for paper. For the purposes of the inventionreactive sizes for paper are, for example, alkyldiketenes,alkenylsuccinic anhydrides, alkyl isocyanates or chloroformic esters offatty alcohols, ester alcohols and/or carboxamido alcohols.Alkyldiketenes suitable for the preparation of the fixing agents may becharacterized, for example, with the aid of the following formula:

where

R¹, R²=H, C₁-C₂₂-alkyl, C₁₀-C₂₂-alkenyl, C₄-C₈-cycloalkyl, aryl oraralkyl.

R¹ and R² in the formula IV are preferably identical or different alkylor alkenyl radicals of 14 to 22 carbon atoms. These compounds are usedas they are or in the form of aqueous dispersions for the preparation ofthe fixing agents.

Preferred aqueous dispersions of reactive sizes contain, as reactivesizes, C₁₄-C₂₂-alkyldiketenes and, as protective colloids, reactionproducts of polymers containing vinylamine units with diketenes of theformula IV.

Such dispersions contain, for example, stearyldiketene, lauryldiketene,palmityldiketene, oleyldiketene, behenyldiketene or mixtures thereof assizes and reaction products of hydrolyzed polymers of N-vinylformamidewith stearyldiketene, lauryldiketene, palmityldiketene, oleyldiketene,behenyldiketene or mixtures thereof as protective colloids.

The aqueous dispersions of reactive sizes can, if required, bestabilized with other reactive colloids. Examples of suitable protectivecolloids are the conventional water-soluble or water-dispersiblepolymeric protective colloids, eg. cationic, amphoteric and/or anionicstarch. The aqueous dispersions of reactive sizes preferably containfrom 10 to 25% by weight of reactive size and preferably from 1 to 3.5%by weight of at least one protective colloid or dispersant, for exampleligninsulfonic acid, condensates of naphthalenesulfonic acid andformaldehyde, sulfonated polystyrene, C₁₀-C₂₂-alkylsulfonic acids,C₁₀-C₂₂-alkylsulfuric acids and salts and mixtures of the statedcompounds. They can, if required, contain further assistants, such asmono-, di- and triglycerides, fatty acids and their esters or amides,which are known in the literature as stabilizers for alkyldiketenedispersions.

Other suitable reactive sizes are cyclic dicarboxylic anhydrides of theformula

where

R is C₅-C₂₂-alkyl or C₅-C₂₂-alkenyl and

n is 1 or 2.

Examples of anhydrides of the formula V are decenylsuccinic anhydride,octenylsuccinic anhydride, dodecenylsuccinic anhydride andn-hexadecenylsuccinic anhydride.

Further suitable reactive sizes are organic isocyanates, such asC₁₂-C₃₆-alkyl isocyanates, for example dodecyl isocyanate, octadecylisocyanate, tetradecyl isocyanate, hexadecyl isocyanate, eicosylisocyanate, docosyl isocyanate, and decyl isocyanate.

Further suitable reactive sizes are chloroformic esters of esteralcohols, fatty alcohols and/carboxamido [sic] alcohols. Such reactivesizes are described, for example, in DE-A-33 01. The abovementionedsizes, such as alkyldiketenes, cyclic carboxylic anhydrides and organicisocyanates, are described in DE-B-27 10 061.

For the preparation of the fixing agents, the amino- and/orammonium-containing polymers described above are reacted with thecompounds known as reactive sizes for paper in a weight ratio of polymerto reactive size of from 15,000:1 to 1:5, preferably from 1000:1 to 1:1.Preferably used fixing agents are prepared by reacting uncrosslinkedpolymers selected from the group consisting of the

polymers containing vinylamine units and/or

polyethyleneimines

with C₁₄-C₂₂-alkyldiketenes, cyclic C₅-C₂₂-alkylsuccinic anhydrides orC₅-C₂₂-alkenylsuccinic anhydrides. The reaction of the amino-containingpolymers with the substances known as reactive sizes is usually carriedout by thoroughly mixing the reactive size or solution or aqueousdispersion of a reactive size with an aqueous solution of an aminoand/or ammonium-containing polymer at, for example, from 20 to 100° C.,preferably from 40 to 70° C., and allowing the reaction to continueuntil the reactive size used has completely reacted. The reactionproducts thus obtained are used as fixing agents in the production ofpaper, board and cardboard. The fixing agents are used in an amount of,for example, from 0.01 to 2, preferably from 0.02 to 1, % by weight,based on dry paper stock. Surprisingly, with the fixing agents usedaccording to the invention, the fixation of water-soluble andwater-insoluble interfering substances in the paper is substantiallyimproved compared with the prior art.

In a preferred embodiment of the process, the drainage of the parerstock is additionally carried out in the presence of a retention aid. Inaddition to anionic retention aids or nonionic retention aids, such aspolyacrylamides, cationic polymers are preferably used as retention aidsand as drainge aids. This results in a significant improvement in therunnability of the paper machines. All products commercially availablefor this purpose can be used as cationic retention aids. These are, forexample, cationic polyacrylamides, polydiallyldimethylammoniumchlorides, polyethyleneimines, polyamines having a molar mass of morethan 50,000, polyamines which may be modified by grafting onethyleneimine, polyetheramides, polyvinylimidazoles,polyvinylpyrrolidines, polyvinylimidazolines,polyvinyltetrahydropyrines, poly(dialkylaminoalkyl vinyl ethers),poly(dialkylaminoalkyl (meth)acrylates) in protonated or quaternizedform and polyamidoamines of adipic acid and polyalkylenepolyamines suchas diethylenetriamineamine [sic], which are grafted with ethylenimineand crosslinked with polyethylene glycol dichlorohydrin ethers accordingto DE-B-24 34 816, or polyamidoamines which are reacted withepichlorohydrin to give water-soluble condensates, and copolymers ofacrylamide or methacrylamide and dialkylaminoethyl acrylates ormethacrylates, for example copolymers of acrylamide anddimethylaminoethyl acrylate in the form of a salt with hydrochloric acidor in the form quaternized with methyl chloride.

The cationic polymers which are used as retention aids have FikentscherK values of at least 140 (determined in 5% strength aqueous sodiumchloride solution at a polymer concentration of 0.5% by weight, at 25°C. and at a pH of 7).

The drainage of the paper stock in the presence of the fixing agents tobe used according to the invention is preferably additionally effectedin the presence of

polymers containing vinylamine units

ethyleneimine-grafted and crosslinked polyamidoamines

polyacrylamides and/or

polydiallyldimethylammonium chlorides

as retention aids. The retention aids are preferably used in amounts offrom 0.01 to 0.2% by weight, based on dry paper stock. The ratio offixing agent to retention aid is, for example from 1:2 to 5:1. Comparedwith conventional combinations of fixing agents and cationic retentionaids, improved retention and accelerated drainage of the paper stock areachieved by the novel process.

In the examples which follow, percentages are by weight unless statedotherwise. The K values were determined according to H. Fikentscher,Cellulose-Chemie, Vol. 13, (1932) 58-64 and 71-74 in 5% aqueous sodiumchloride solution at 25° C. and at a pH of 7 and at a polymerconcentration of 0.5% by weight. The molar masses of the polymers weremeasured by light scattering.

The chemical oxygen demand (COD) was determined according to DIN 38 409.The light transmittance (optical transparency) of the white water wasmeasured using a Dr Lange photometer at a wavelength of 588 nm. It is ameasure of the retention of fines and fillers and is stated in %. Thehigher the value of the light transmittance, the better is theretention.

Preparation of the Fixing Agents

Fixing Agent 1

500 g of an aqueous polyethyleneimine solution having a solids contentof 49% and an average molecular weight of 750,000 are initially taken ina 2 l flask equipped with a stirrer and a thermometer and are heated to70° C. Thereafter, 1.78 g of stearyldiketene are added with thoroughstirring and the mixture is then stirred for a further hour at 70° C.,cooled to room temperature and brought to a pH of 7 by adding formicacid. A 49.1% strength aqueous solution having a viscosity of 754 mPasis obtained.

Fixing Agent 2

1000 g of an aqueous solution of polyvinylformamide having a polymercontent of 16.5% are initially taken in a stirred apparatus equippedwith a reflux condenser, a thermometer and a dropping funnel and areheated to 80° C. with thorough stirring. The K value of thepolyvinylformamide is 87 (Mw=250,000, ≈2321 mmol of vinylformamideunits.). 102 g (about 1275 mmol) of 50% strength aqueous sodiumhydroxide solution are added dropwise in the course of 20 minutes. Thereaction mixture is then stirred for a further hour at 80° C. Aftercooling to room temperature, the solution is freed from the sodiumformate by dialysis and is concentrated by distillation. 1120 g of anaqueous polymer solution having a polymer content of 11.4% are obtained.The polymer contains 57 mol % of vinylamine units and 43 mol % ofvinylformamide units.

600 g of the polymer solution described above are initially taken in astirred apparatus, brought to pH 9 and heated to 80° C. As soon as thistemperature has been reached, 4.40 g of stearyldiketene in the form of amelt are added dropwise. The mixture is then stirred for a further 2hours at 80° C. and then cooled to room temperature. A 12% strengthaqueous solution having a viscosity of 1065 mPas is obtained.

Fixing Agent 3

As described in the preparation of fixing agent 2, 1000 g of an aqueouspolyvinylformamide solution having a polymer content of 16.5% by weightand a K value of the polymer of 87 are initially taken in a stirredapparatus and 204 g of 50% strength aqueous sodium hydroxide solutionare added to eliminate the formyl groups from the polymer. The reactiontime is 2 hours at 80° C. Thereafter, the solution is cooled to roomtemperature, freed from sodium formate by means of dialysis andconcentrated by distillation. 1390 g of a polymer solution having apolymer content of 7.4% are obtained. The polymer is 95% hydrolyzed andthus contains 95% of vinylamine units and 5 mol % of vinylformamideunits.

600 g of the polymer solution described above are brought to pH 9 andheated to 80° C. while stirring. As soon as this temperature has beenreached, 4.60 g of stearyldiketene in the form of a melt are added. Themixture is then stirred for a further 2 hours at 80° C. and then cooledto room temperature. An 8% strength aqueous solution having a viscosityof 912 mPas is obtained.

Fixing Agent 4

600 g of an aqueous polyethyleneimine solution having a solids contentof 49% and an average molecular weight of 750,000 are initially taken ina 2 l flask equipped with a stirrer and a thermometer and heated to 50°C. Thereafter, 56 g of an aqueous 2% dispersion of octadecenylsuccinicanhydride are added with thorough stirring, and the reaction mixture isstirred for a further hour at 50° C. Thereafter, the mixture is cooledand formic acid is added until the pH is 7. A 44.9% strength aqueoussolution having a viscosity of 1045 mPas is obtained.

Fixing Agent 5

600 g of an aqueous polyethyleneimine solution having a solids contentof 49% and an average molecular weight of 750,000 are initially taken ina 2 l flask equipped [lacuna] stirrer and thermometer and are heated to50° C. As soon as this temperature has been reached, 17.8 g of a 10%aqueous dispersion of stearyldiketene are added with thorough stirring,and the reaction mixture is stirred for a further hour at 50° C.Thereafter, it is cooled and brought to pH 7 by adding formic acid. A47.5% strength aqueous solution having a viscosity of 598 mPas isobtained.

Comparative Example 1 (According to Example 1 of WO-A-94/12560)

Fixing Agent 6

799 g of an anhydrous polyethyleneimine having an average molecularweight of 25,000 are initially taken in a flask equipped with a stirrer,thermometer and means for working under nitrogen and are heated to 140°C. under a nitrogen stream. 69 g of propionic acid are added in thecourse of 30 minutes. The temperature is then increased to 180° C. Thewater formed in the reaction is continuously separated off over a periodof 5 hours. 200 g of the polymer prepared in this manner are dilutedwith 700 ml of water and heated to 70° C. 36.5 ml of a 21% strengthaqueous solution of a bischlorohydrin polyethylene glycol having amolecular weight of 400 are then added a little at a time in the courseof 3 hours. The reaction mixture is stirred for a further hour at 70° C.after the addition of the crosslinking agent and then brought to pH 8 byadding 85 g of an 85% strength formic acid. 1018 g of a 20.7% strengthpolymer solution having a viscosity of 884 mPas are obtained.

EXAMPLES Examples 1 to 5

An aqueous fiber suspension comprising TMP (thermomechanical pulp) andhaving a consistency of 2% was divided into equal portions and anaqueous solution of 5% humic acid was added as an interfering substancein each case.

The amounts of fixing agents 1 to 6 shown in Table 1 and in addition0.2% by weight, based on dry fiber, of a cationic polyacrylamide havinga K value of 240, as a retention aid, were added to each of the samplesof this pulp. After thorough mixing and filtration of the flocculatedpaper stock, the absorbance of the alkaline filtrate is determined at awavelength of 340 nm. The results are shown in Table 1.

TABLE 1 Example 0.05% Absorbance 0.1% Absorbance 1 Fixing agent 1 0.30Fixing agent 1 0.19 2 Fixing agent 2 0.38 Fixing agent 2 0.16 3 Fixingagent 3 0.30 Fixing agent 3 0.17 4 Fixing agent 4 0.40 Fixing agent 40.22 5 Fixing agent 5 0.20 Fixing agent 5 0.27 Comp.- Fixing agent 60.49 Fixing agent 6 0.26 Example 1

Comparative Example 2

The paper stock containing formic acid was filtered directly, ie. in theabsence of fixing agents and retention aids. The absorbance of thefiltrate was 1.20.

Examples 6 to 10

An aqueous fiber suspension comprising TMP (thermomechanical pulp) andhaving a consistency of 2% was divided into equal portions, and a woodextract (2 ml/75 ml of TMP) as an interfering substance was added ineach case. The amounts of fixing agents shown in Table 2, followed by0.2%, based on dry fiber, of a commercial cationic polyacrylamide havinga K value of 240, as a retention aid were added to each of the samplesof this pulp. After thorough mixing and filtration of the flocculatedpaper stock, the absorbance of the alkaline filtrate was determined at340 nm. The results are shown in Table 2.

TABLE 2 Metering of ... Fixing agent (calculated Fixing as 100%) Exampleagent 0% 0.03% 0.05% 0.1% 6 1 1.20 0.37 0.35 0.30 7 2 1.21 0.33 0.320.22 8 3 1.18 0.42 0.35 0.28 9 4 1.20 0.44 0.39 0.29 10 5 1.20 0.28 0.240.20 Comp. 6 1.19 0.45 0.42 0.33 Example 3

Comparative Example 4

The paper stock described in Examples 6 to 10 is drained without furtheradditives. The absorbance of the alkaline filtrate was 0.51.

Examples 11 to 15

0.15 g/l of an aqueous dispersion of coated waste was added asinterfering substance (sticky interfering substance) to samples of anaqueous fiber suspension comprising TMP (thermomechanical pulp) andhaving a consistency of 2%. The amounts of fixing agents shown in Table3 and 0.2%, based on dry fiber, of a commercial cationic polymer, havinga K value of 240, as a retention aid, were then added to each of thesamples of this pulp. After thorough mixing and filtration of theflocculated paper stock, the number of particles was determined in thefiltrate with the aid of a laser optical method (cf. Nordic Pulp & PaperResearch Journal, No. 1-1994, 9 (1994), pages 26 to 30, 36). The resultsare shown in the table.

TABLE 3 Fixing Metering of ... % fixing agent (100%) Example agent 0%0.01% 0.02% 0.05% 0.1% 11 1 100 77 63 18 2 12 2 100 69 42 27 7 13 3 10078 47 14 8 14 4 100 89 52 24 10 15 5 100 68 45 19 7 Comp. 6 100 91 61 3362 Exam- ple 5

We claim:
 1. A process for the production of paper, board and cardboard,comprising: draining a paper stock containing interfering substances inthe presence of an uncrosslinked fixing agent which is a reactionproduct prepared by reacting an amino- or ammonium-containing polymerselected from the group consisting of: a polymer containing vinylamineunits, a polyalkylenepolyamine, a polyamidoamine, anethyleneimine-grafted polyamidoamine, a polydiallyldimethylammoniumchloride, a polymer containing dialkylaminoalkylacrylamide units ordialkylaminomethacrylamide units, a polyallylamine, and a dicyandiamideand formaldehyde condensate, with a reactive size for paper in a weightratio of polymer to reactive size ranging from 15,000:1 to 1:5, theuncrosslinked fixing agent fixing water-soluble interfering substances,colloidal interfering substances and water-insoluble tacky impurities tothe fibers of the paper stock.
 2. The process as claimed in claim 1,wherein the uncrosslinked fixing agent is a reaction product prepared byreacting amino-containing compounds with a reactive sizing agent in aweight ratio ranging from 1,000:1 to 1:1.
 3. The process as claimed inclaim 1, wherein said fixing agent is employed in an amount ranging from0.01 to 2% by weight relative to the weight of dry paper stock.
 4. Theprocess as claimed in claim 1, wherein said reactive size is a compoundselected from the group consisting of an alkyldiketene, analkenylsuccinic anhydride, an alkyl isocyanate and a chloroformic esterof a fatty alcohol, an ester alcohol or a carboxamido alcohol.
 5. Theprocess as claimed in claim 1, wherein said drainage of said paper stockis additionally conducted in the presence of a retention aid.
 6. Theprocess as claimed in claim 1, wherein said fixing agent is a reactionproduct prepared by reacting: a polymer containing vinylamine units, ora polyethyleneimine with a C₁₄-C₂₂-alkyldiketene, a cyclicC₅-C₂₂-alkylsuccinc anhydride or a C₅-C₂₂-alkenylsuccinic anhydride. 7.The process as claimed in claim 1, wherein the draining of the paperstock is additionally conducted in the presence of: a polymer containingvinylamine units, an ethyleneimine-grafted and crosslinkedpolyamidoamine, a polyacrylamide, or a polydiallyldimethylammoniumchloride as a retention aid.